svn commit: r308553 - head/sys/dev/ioat

[Conrad E. Meyer]

Author: cem
Date: Fri Nov 11 20:09:54 2016
New Revision: 308553
URL: https://svnweb.freebsd.org/changeset/base/308553

Log:
  ioat(4): Fix race between process_events and reset_hw
  
  In the case where a hardware error is detected during
  ioat_process_events, hardware may advance (by one descriptor, probably)
  and a subsequent ioat_process_events may race the intended ioat_reset_hw
  followup.  In that case, the second process_events would observe a
  completion update that does not match the software "last_seen" status,
  and attempt to successfully complete already-failed descriptors.
  
  Guard against this race with the resetting_cleanup flag.
  
  Reviewed by:	bdrewery, markj
  Sponsored by:	Dell EMC Isilon

Modified:
  head/sys/dev/ioat/ioat.c

Modified: head/sys/dev/ioat/ioat.c
==============================================================================
--- head/sys/dev/ioat/ioat.c	Fri Nov 11 20:08:45 2016	(r308552)
+++ head/sys/dev/ioat/ioat.c	Fri Nov 11 20:09:54 2016	(r308553)
@@ -765,6 +765,15 @@ out:
 	mtx_lock(&ioat->submit_lock);
 	mtx_lock(&ioat->cleanup_lock);
 	ioat->quiescing = TRUE;
+	/*
+	 * This is safe to do here because we have both locks and the submit
+	 * queue is quiesced.  We know that we will drain all outstanding
+	 * events, so ioat_reset_hw can't deadlock.  It is necessary to
+	 * protect other ioat_process_event threads from racing ioat_reset_hw,
+	 * reading an indeterminate hw state, and attempting to continue
+	 * issuing completions.
+	 */
+	ioat->resetting_cleanup = TRUE;
 
 	chanerr = ioat_read_4(ioat, IOAT_CHANERR_OFFSET);
 	if (1 <= g_ioat_debug_level)